I think that has never happened to me on non-LiquidThreads discussion pages, but looking at the page source it embeds/transcludes https://fr.wikipedia.org/wiki/Wikip%C3%A9dia:Questions_techniques/semaine_16_2015 so I wonder if this is directly related to the template / transclusion use.

In my opinion, Purging is a poor workaround and should never be prominently advertised. I'm not fully convinced that purging is actually needed here - did you try to bypass your browser cache instead?

One part of the problem is the server giving a page out-of-date.

This part is so big that a workaround has been made against it: purge.

Then a second part of the problem is the page not giving any way to do the purge.

I did bypass the cache of my navigator. Result: NOK.

Then I purged the page, with action=purge. Result: OK.

I'd love to know if other users of that very page experience the same problem (though I assume the answer is likely a "yes").

As I explained before: Offering a default UI option to purge a page is out of question. If you feel strongly that there should be, this could be implement by a link on that very page itself.

I also encounter this issue often on templates, after editing the doc — although these pages do usually give a way to purge.

This issue also occurs on a template that calls a module.

I have edited the module. But the template still shows the result of the old module.

See also:

T98582: The page displays a broken call to the template A when the needed template redir B was created recently, and the page gives no way to purge it